Toward truly combined PET/CT imaging using PET detectors and photon counting CT with iterative reconstruction implementing physical detector response

• Published in: Medical physics (Lancaster) 2012-09, Vol.39 (9), p.5697-5707
• Main Authors: Thibaudeau, Christian, Bérard, Philippe, Tétrault, Marc-André, Leroux, Jean-Daniel, Bergeron, Mélanie, Fontaine, Réjean, Lecomte, Roger
• Format: Article
• Language: English
• Subjects: biomedical electronics; Computed tomography; data acquisition; Data acquisition and logging; Digital computing or data processing equipment or methods, specially adapted for specific applications; dual modality; experimental system matrix; filters; Image data processing or generation, in general; Image detection systems; Image Processing, Computer-Assisted - methods; image reconstruction; image registration; image resolution; Image sensors; iterative methods; iterative reconstruction; Medical image noise; medical image processing; Medical image reconstruction; Medical imaging; Medical X‐ray imaging; Multimodal Imaging - instrumentation; Multimodal Imaging - methods; phantoms; photon counting; photon counting CT; Photons; Positron emission tomography (PET); positron emission tomography/computed tomography (PET/CT); Positron-Emission Tomography; Reconstruction; Registration; Spatial resolution; Tomography, X-Ray Computed; X‐ray detectors
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.4747265

Purpose: This paper intends to demonstrate the feasibility of truly combined PET/CT imaging and addresses some of the major challenges raised by this dual modality approach. A method is proposed to retrieve maximum accuracy out of limited resolution computed tomography (CT) scans acquired with positron emission tomography (PET) detectors. Methods: A PET/CT simulator was built using the LabPET™ detectors and front-end electronics. Acquisitions of energy-binned data sets were made using this low spatial resolution CT system in photon counting mode. To overcome the limitations of the filtered back-projection technique, an iterative reconstruction library was developed and tested for the counting mode CT. Construction of the system matrix is based on a preregistered raster scan from which the experimental detector response is obtained. PET data were obtained sequentially with CT in a conventional manner. Results: A meticulous description of the system geometry and misalignment corrections is imperative and was incorporated into the matrix definition to achieve good image quality. Using this method, no sinogram precorrection or interpolation is necessary and measured projections can be used as raw input data for the iterative reconstruction algorithm. Genuine dual modality PET/CT images of phantoms and animals were obtained for the first time using the same detection platform. Conclusions: CT and fused PET/CT images show that LabPET™ detectors can be successfully used as individual X-ray photon counting devices for low-dose CT imaging of the anatomy in a molecular PET imaging context.